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The smallest natural number by which 1620 must be multiplied to make a perfect square is:
A{'text': '3'}
B{'text': '6'}
C{'text': '5'}
D{'text': '10'}
Answer & Solution
Correct answer: C. {'text': '5'}
1. Factorise 1620 = 2² × 3⁴ × 5.
2. The factor 5 appears only once — it lacks a pair.
3. Multiplying by 5 gives 1620 × 5 = 8100 = 2² × 3⁴ × 5², a perfect square.
4. Verification: √8100 = 90 ✓.
5. Hence the smallest required multiplier is **5**.
_Source: Selina Concise ICSE Class 8 Mathematics Ch 3 "Squares and Square Roots", Prime factorisation method_
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